As for steep, projected increases in CO2 levels over the next century, Lowenstein thinks that might not be our only cause for concern.
"If we assume that you and I are both in our 50s, the change in atmospheric CO2 in our lifetime is greater than the rate of any change in at least the last half million years," said Lowenstein, who is particularly concerned about unexpected changes
"Right now, we're on a predictable pace. But there will likely be tipping points, unexpected events that could really change things, so all of a sudden we may get changes in ocean circulation that we never would have predicted, or the tundra may melt. Some unexpected event is going to occur that's going to be more dramatic than the progressive changes that occurred over the last 100 years."
As a scientist, Lowenstein has no doubt that burning oil, gas and coal are fueling global warming and creating, along with environmental degradation, an immediate threat to some species of life on the planet. His opinion is unchanged by those who would point to the earth's ancient hothouse past as proof that natural swings in climate take place with or without human intervention.
Lowenstein said these consequences seem more and more likely without drastic change.
"The glacier on Mount Kilimanjaro has not much time left even now. Many mountain glaciers are going to disappear," he said. "It all depends on how much fossil fuel we burn. But if we keep doing what we're doing now, we will be up to the CO2 levels of the Eocene within another 100 or 200 years."
As Lowenstein points out, although it is difficult to predict how global temperatures over the coming centuries will compare to the Eocene, the "hothouse" world 50 million years ago should serve as a reminder of
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